Typically, in known gasoline dispensing nozzles, a mechanical lever apparatus is utilized to control a main valve in the nozzle to thereby controllably dispense fuel, such as gasoline, from a storage tank to the fuel tank of a motor vehicle. The nozzle is coupled to a hose which is, in turn, coupled to the storage tank. A pressurizing device such as a pump is arranged to cause a pressurized fluid flow, from the storage tank through the hose and into the nozzle. A tubular spout extends from the nozzle and is arranged and configured for reception into an intake pipe of the motor vehicle fuel tank to dispense the fuel into the fuel tank. For safety reasons, particularly in self-service stations, an overflow protection mechanism is provided to automatically close the main valve of the nozzle when the fuel tank is filled and the fuel level rises to above the lower end of the spout inserted into the intake pipe. In fuel dispensing nozzles in commercial use, the automatic valve shut-off mechanism comprises a mechanical device controlled by the so-called "venturi" effect.
To use the venturi effect, a small opening is formed in a wall of the fluid flow channel of the nozzle to provide an air passage from the outside environment, which is at normal atmospheric pressure, to the fluid flow channel. Due to the venturi effect, the passage of fluid through the fluid flow channel causes a reduction in pressure in the air passage resulting in a flow of air from the outside environment, now at a higher pressure than the pressure at the channel opening, through the opening and into a series of tubes and cavities built into the nozzle. The flow of air continues as long as fluid is flowing through the nozzle.
One of the cavities through which the air flows is a cylindrical cavity having a flexible diaphragm formed at its base, with the other cavity walls being rigid and non-flexible. The outer side of the diaphragm is exposed to normal atmospheric pressure. A spring mechanism is employed to exert enough pressure on the diaphragm from the cavity side to distort and hold the diaphragm in a normally concave geometry, so that an element mechanically coupled to the diaphragm, on the opposite side of the spring, will be held in a stable position at a fraction of an inch (typically in the order of 0.2 inches to 0.4 inches) from the plane of the undistorted diaphragm.
As long as the flow of air is undisturbed, the pressure differential across the diaphragm due to the flowing air is minimal and is not enough to overcome the effect of the spring. Thus, in normal operation, the spring will keep the diaphragm in the distorted concave configuration, both while the nozzle is not active (no fluid flow), and while fluid is flowing through the nozzle. In this position, a mechanical connection is established which permits a pivot stem to be held rigidly in place so that an axis can be established at the end of the pivot stem which acts as a pivot point for a user-actuated lever arm. The main flow control valve of the nozzle is activated by a valve stem which is positioned so that when the lever arm is rotated by a user about the pivot point provided by the pivot stem, the valve stem of the main valve is forced open against the action of a biasing spring arranged on the opposite side of the valve. The biasing spring exerts a mechanical force on the valve stem that is sufficient to close the valve when the lever force is removed.
The venturi switching effect is realized when the air flow through the air passages is interrupted for any reason while the fluid flow continues. To use the venturi effect to stop the fluid flow when the fluid level reaches the nozzle, the air passage begins near the tip of the nozzle and includes an air tube which passes down to the tip of the nozzle spout, usually inside the nozzle spout. As soon as the fluid level in the fuel tank intake pipe of a motor vehicle reaches the nozzle spout, the opening of the air tube is covered by the fluid and the flow of air is inhibited.
The venturi effect of the continuing fluid flow passing by the opening in the fluid delivery channel then causes a rapid decrease in pressure throughout the air passage, which results in a substantial pressure differential across the diaphragm. The pressure differential is great enough to overcome the force of the diaphragm spring and thus forces the diaphragm into a relatively convex geometry within the cavity, thereby moving the surface of the center of the diaphragm enough to disengage the parts, as for example, the pivot stem, which normally form the mechanical connection permitting the user-operated valve lever to pivot around the pivot point.
The parts, which are normally held in place by the spring action on the diaphragm, are normally designed with bearings such that an orthogonal displacement is easily accomplished. When these parts are removed from the pivot stem, the pivot stem is caused to move to a position allowing the lever arm to freely pivot around the valve stem such that no force can be applied to the valve stem via the lever. Since no force can be applied to the valve stem by the lever, the biasing spring, which acts against the opening of the valve, forces the valve stem into a valve shut-off position and no fluid can be dispensed through the nozzle. The biasing spring is also sufficiently rigid to act as a pivot point for the lever after the pivot stem is moved from its pivot point position.
There are a number of disadvantages in the use of venturi switching. For example, before the venturi effect can occur, some fluid flow must occur to cause the pressure differential across the diaphragm in the air passage. This can result in a "splash-back" effect that occurs when a determined user constantly "jockeys" the lever, after the fuel level has reached the nozzle spout, to restart fluid flow.
Moreover, an intricate mechanical design is required. The air passage has to be designed such that fuel will not flow out of the fluid flow channel and into the air passage, yet the air passage must accommodate air flow from outside the nozzle and into the fluid flow channel. The need for an intricate interface between the fuel channel and the outside air requires relatively complex machine work in the fabrication of the nozzle, which substantially affects the cost of manufacture of even a simple nozzle. Other known nozzles have been proposed to eliminate a venturi type valve shut down. However, it is not believed that such other prior art has been used successfully in a commercial application.